dhcp: clone hardware addresses throughout

I still noticed DHCP requests with incorrect MAC source addresses.
Turns out there were still a number of incorrect HardwareAddr usages.

Author: stapelberg

cmd/dhcp4/dhcp4.go

@@ -28,6 +28,7 @@ import (
 	"os"
 	"os/signal"
 	"path/filepath"
+	"slices"
 	"syscall"
 	"time"
 
@@ -97,7 +98,8 @@ func logic() error {
 	if err != nil {
 		return err
 	}
-	hwaddr := iface.HardwareAddr
+	// Clone the hardware address as the backing array does not remain valid.
+	hwaddr := slices.Clone(iface.HardwareAddr)
 	// The interface may not have been configured by netconfigd yet and might
 	// still use the old hardware address. We overwrite it with the address that
 	// netconfigd is going to use to fix this issue without additional

internal/dhcp4/dhcp4.go

@@ -103,7 +103,8 @@ func (c *Client) ObtainOrRenew() bool {
 			return
 		}
 		if c.hardwareAddr == nil && c.HWAddr != nil {
-			c.hardwareAddr = c.HWAddr
+			// Clone the hardware address as the backing array does not remain valid.
+			c.hardwareAddr = slices.Clone(c.HWAddr)
 		}
 		if c.hardwareAddr == nil {
 			// Defensive slices.Clone because I noticed c.hardwareAddr

internal/dhcp6/dhcp6.go

@@ -19,6 +19,7 @@ import (
 	"fmt"
 	"log"
 	"net"
+	"slices"
 	"strconv"
 	"time"
 
@@ -115,9 +116,10 @@ func NewClient(cfg ClientConfig) (*Client, error) {
 		}
 	}
 
-	hardwareAddr := iface.HardwareAddr
+	// Clone the hardware address as the backing array does not remain valid.
+	hardwareAddr := slices.Clone(iface.HardwareAddr)
 	if cfg.HardwareAddr != nil {
-		hardwareAddr = cfg.HardwareAddr
+		hardwareAddr = slices.Clone(cfg.HardwareAddr)
 	}
 
 	var duid *dhcpv6.Duid